I was actually looking for some RW-6 rings a while ago and came across Cirrus Hardware in the UK that currently makes them. On their website, Part 1083 (RW-6) rings. They were $15/ea and freight to WA was $35 and 4 days for 1-7 pieces.
I never ordered them as I got sidetracked from that project.
This is a little off topic but since they were mentioned, I figured I would chime in as it took a bit of searching to find them.